So far, only diamondback moths, which were used in this study, have developed resistance to Bt toxins in the field. The resistance resulted from farmers and gardeners spraying Bt toxin on plants for insect control, a long-standing practice. While Bt toxin sprayed on leaves quickly degrades in sunlight and often does not reach the insect, genetically modified (GM) Bt plants express the bacterium in the plant tissue, which makes Bt plants especially effective against insects that bore into stems, such as the European corn borer, which causes more than $1 billion in damage annually in the United States.
In greenhouses at the New York State Agriculture Experiment Station in Geneva, N.Y., the researchers used three types of GM broccoli plants: two types of plants each expressed a different Bt toxin, and a third -- known as a pyramided plant -- expressed both toxins. Elizabeth Earle and Jun Cao, co-authors of the PNAS paper and members of the Department of Plant Breeding and Genetics at Cornell created the plants.
For their studies, the researchers employed strains of diamondback moth that were resistant to each of the Bt proteins. The combination of Bt plants and Bt-resistant insects allowed them to explore the concurrent use of single- and dual-gene Bt plants in a way that could not be done with cotton or maize, although their results are relevant to these widely grown plants.
First, the researchers bred moth populations in which a low percent of the moths were resistant to a single Bt toxin. The insects were then released into caged growing areas with either single-gene plants, dual-gene plants or mixed populations and allowed to reproduce for two years.
The researchers found that after 26 generations of the insect living in the greenhouse wit
Source:Cornell University News Service